BE AND FE WEBSOCKET

import grails.transaction.Transactional
import org.springframework.messaging.simp.SimpMessageSendingOperations

class MyController {

    MyService myService
    SimpMessageSendingOperations messagingTemplate

    @Transactional
    def addItems() {
        def items = request.JSON.items
        myService.addItemsToList(items) { progress ->
            messagingTemplate.convertAndSend("/topic/progress", [percent: progress])
        }
    }
}
------------------
import org.springframework.stereotype.Service

@Service
class MyService {

    List<String> itemsList = []

    def addItemsToList(List<String> items, Closure progressCallback) {
        items.eachWithIndex { item, i ->
            itemsList << item
            progressCallback(100.0 * (i + 1) / items.size())
        }
    }
}
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import grails.transaction.Transactional
import org.springframework.messaging.simp.SimpMessageSendingOperations

class MyController {

    MyService myService
    SimpMessageSendingOperations messagingTemplate

    @Transactional
    def addItems() {
        def items = request.JSON.items
        myService.itemsList = []
        myService.addItemsToList(items)
    }
}
--------------
import org.springframework.stereotype.Service

@Service
class MyService {

    List<String> itemsList = []
    SimpMessageSendingOperations messagingTemplate

    def addItemsToList(List<String> items) {
        items.eachWithIndex { item, i ->
            itemsList << item
            messagingTemplate.convertAndSend("/topic/progress", [percent: (100.0 * (i + 1) / items.size())])
        }
    }
}
-----------

FE

// Create a WebSocket connection to the server
const socket = new SockJS('/ws');
const stompClient = Stomp.over(socket);

// Connect to the server
stompClient.connect({}, function () {
    // Subscribe to the "/topic/progress" topic
    stompClient.subscribe('/topic/progress', function (message) {
        // Parse the progress information from the message
        const progress = JSON.parse(message.body);
        console.log(`Progress: ${progress.percent}%`);
    });
});